In regard to an exhaust recirculation system (EGR system) wherein a part of the exhaust is recirculated into the intake air to perform combustion control of an internal combustion engine, various devices have been proposed to promote mixing of intake air and recirculated exhaust gas.
Jikkai Hei 3-114563 published by the Japanese Patent Office in 1991 discloses a system wherein an insulator is gripped between a throttle case and surge tank in the intake passage of the engine, a pair of exhaust inlets are provided at an 180-degree interval in the insulator towards the center of the intake passage, and exhaust gas is mixed with intake air through these exhaust gas inlets.
Jikkai Hei 3-114564 published in 1991 by the Japanese Patent Office discloses a device wherein an annular passage for leading exhaust gas surrounds the intake passage, and exhaust gas is led into the intake air via plural holes connecting the annular passage and intake passage.
Tokkai Hei 5-106519 published by the Japanese Patent Office in 1993 discloses a system wherein a minute throughhole connecting an exhaust port and intake port of an engine.
Further, this prior art discloses that the air-fuel mixture of fuel injected into the intake port and intake air is heated by the exhaust gas led to the intake port, and a swirl promoted by the throughhole arranged on a tangential line of the cross-section of the inlet port accelerates evaporation of the fuel adhering to the wall of the inlet port.